The present invention generally relates to a laser of the type in which a cantilevered capillary bore tube is used to maximize laser power output and, more particularly, to a structure for supporting the free end of the cantilevered tube in an improved manner.
Gas lasers, such as of the helium-neon type disclosed in U.S. Pat. No. 4,644,554 to Sheng and assigned to the assignee of the present invention, typically have a sealed outer cylindrical envelope with two reflective mirrors located at opposite ends thereof. The mirrors are positioned to face each other along a central axis and define an optical resonant cavity therebetween. A capillary bore tube placed in the cavity is used to confine the discharge between an anode and cathode in the outer envelope to maximize laser power output. The bore tube is centrally mounted in cantilevered fashion within the outer envelope in axial alignment with the central axis of the mirrors. In particular, one end of the capillary bore tube is fixedly attached to one end of the outer envelope, whereas the other end of the bore tube is a free end, unsupported directly by the envelope.
During operation of the laser, the capillary bore tube is heated to a substantially higher temperature than the temperature reached by the outer envelope. Since the bore tube is subjected to a higher temperature than the outer envelope, the length of the bore tube increases at a greater rate than the length of the outer envelope. The free end of the bore tube must therefore be permitted to shift longitudinally with respect to the outer envelope in alignment with the central axis to accommodate this difference in thermal expansion.
However, transverse or radial shifting of the free end of the bore tube relative to the central axis of the mirrors and cavity defined therebetween is highly undesirable. Transverse bore tube shifting may result in clipping of a portion of the laser beam and thereby reduce the power output of the laser. It is, therefore, mandatory to provide some means to support the bore tube so as to allow axial longitudinal shifting thereof relative to the outer envelope, but restrain transverse or radial shifting thereof relative to the central axis of the mirrors and thus to the laser beam.
The above-cited Sheng patent discusses several flexible, spring-type spider constructions designed heretofore to provide the means for supporting the bore tube free end. In both of the constructions, the spiders extend between and engage the inside surface of the outer envelope and the outside surface of the bore tube to position the free end transversely within the cavity. However, in one construction the spider is not rigidly attached to the envelope and bore tube to permit the free end of the tube to slide longitudinally within the spider, whereas in the other construction the spider is rigidly attached to the inside surface of the outer envelope and the outside surface of the bore tube but can flex sufficiently to accommodate longitudinal movement of the free end of the tube.
Both constructions have certain drawbacks. The disadvantage of the first construction is that the spider has insufficient transverse rigidity to support relatively high shock loads and vibrations and thereby restrain radial misalignment of the bore tube with the central axis. The disadvantage of the second construction is that the spider can still become detached at certain parts thereof from one or the other of the outer envelope or inner bore tube when sufficiently vibrated, causing misalignment with the central axis upon longitudinal shifting of the bore tube. In both instances, misalignment with the central axis and thereby with the laser beam results in a reduction of the power output of the laser.
Consequently, in view of the above-noted difficulties, as well as others with the spring-like spider constructions of the prior art, it is readily apparent that a need still remains for a structure which supports the capillary bore tube within the laser outer envelope both longitudinally and transversely in the desired manner.